Recently, due to the requirement of a high efficiency and energy-saving technique, power semiconductor devices as examples of the power MOSFET are required to become more and more compact, have a high breakdown voltage, a low on-resistance and low-capacitance. To fulfill this requirement, the technique of locating a field plate electrode in the power semiconductor is gaining attention.
In such semiconductor devices, when voltage between the source and drain is impressed, an electric field is generated between the field plate electrode and drift layer and depletion of the drift layer occurs, and as a result, a high withstand voltage value is created across the source and drain. Moreover, a comparatively high dopant concentration of the drift layer is required to obtain this extent of depletion of the drift layer, and thus, the on-resistance (Ron) across the channel region between the source and drain is reduced (i.e., the leakage current threshold is lower as well).
However, in this type of semiconductor devices, the capacitance (Cgs) between the gate electrode and the field plate electrode increases due to setting of the field plate electrode (FIG. 8) which is not suited to high speed operation and this is a matter of concern. To solve this problem, high speed semiconductors having so called partial type gate structures are gaining attention (FIG. 9). Consequently, such types of semiconductor devices are required to have a higher resistance and higher fabrication yield.